DESCRIPTION: This is a revised re-submission of a competitive renewal application to continue studies on the ionic basis of electrical optical activity in dendritic trees of hippocampal pyramidal cells using probes of intracellular ionic activity. Recent experimental work shows that much Ca entry during synaptic activation is through voltage-dependent Ca channels activated subsequent to Na spiking.This proposal will examine whether specific synaptic inputs and agents affecting potassium channels affect the spatial extent of Ca entry. Strong synaptic stimulation can evoke dendritic Ca spikes, and the effects of synaptic inputs and K channel modulators on propagation of dendritic Ca spikes will be studied. An effort will be made to measure Ca entry through NMDA receptor channels. The types of voltage- dependent Ca channels involved in Ca influx will be examined.